In order to measure power consumed by electric devices which are installed in general homes, shops, small-to-medium sized buildings, etc., it has hitherto been required for professionals to set up a power meter by attaching a voltage transformer or a current transformer to a distribution board, for example. Also, when power consumptions of devices are controlled in a demand system or the like to be held within a predetermined range, work for attaching a power or electrical energy measuring device has been required to be made by professionals, as in the above case, for the measurement of power. Thus, because installation of such a system entails electrical work, the installation needs professionals to carry out the electrical work and pushes up the cost. Further, when trying to install all-electrified appliances in an existing house, such a try has to be abandoned due to a limitation on current allowable for an indoor power line in many cases.
As a related art aiming to cope with the above-described problems, there is known a measuring method using a noncontact type voltmeter. In such a noncontact type voltmeter, a coating of an electric wire, i.e., a target of measurement, is surrounded by a conductor to constitute a capacitor. The conductor (capacitor) and the ground are connected to each other by using two probes of the noncontact type voltmeter. A current flowing between the conductor and the ground and a voltage therebetween are measured in a noncontact manner. Further, means for calculating a voltage correction coefficient is provided and a voltage measuring wire connected to the means is directly connected between a conductive-line exposed portion of the electric wire and the ground by using an alligator clip, for example, to measure a voltage with respect to the ground. The voltage of the electric wire, which has been obtained by the contact measurement, is compared with the voltage of the electric wire, which has been acquired from the noncontact type voltmeter, to determine a phase coefficient and a gain coefficient for the voltage of the electric wire automatically by using a PLL circuit or manually by using a variable capacitor or a variable resistor. The voltage measured in a noncontact manner is corrected based on those coefficients for proper calculation of the voltage (see, e.g., Patent Document 1).
Further, for the purpose of simplifying the work, there is known a measuring device in which a conductive voltage detecting portion having a sharp distal end is provided integrally with a current sensor unit constituting a closed magnetic circuit for easier mounting of the sensor unit (see, e.g., Patent Document 2).
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-55126 (page 4 and FIGS. 1-2)
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2005-134233 (pages 6-7 and FIGS. 1-7)